1. Field of the Invention
The present invention relates to media sensors, and, more particularly, to a method for detecting an absence of print media.
2. Description of the Related Art
One form of a media sensor includes a single light source, such as a light emitting diode (LED), and a light detector, such as a phototransistor. Typically, the light detector is located on the same side of a print media as the light source. During operation, the LED directs light at a predefined angle onto a material surface of the print media, and the surface characteristics of the print media are examined in terms of the amount of light reflected from the surface that is received by the light detector. The presence of the print media is detected based upon a predetermined amount of light reflected from the media to the light detector.
Some media sensors include a pair of light detectors, one of the light detectors being positioned to sense reflected diffuse light and a second detector positioned to sense reflected specular light. Such a sensor may be used, for example, to detect and discriminate between paper media and transparency media.
Media sensors that are used to detect the type of media in an imaging device, such as an ink jet printer, optically measure the glossiness of the media using a media sensor similar to that described generally above. To measure the glossiness, a collimated beam of light is directed towards the media and a reflectance ratio (R) of the detected reflected specular light intensity and the detected diffusively scattered light intensity is calculated. The media sensor is initially calibrated by measuring a reflectance ratio (R0) on a known gloss media. A normalized reflectance ratio (Rn) is calculated using the formula: Rn=(R/R0). Normalized reflectance ratio Rn then is used to identify the media type of an unknown media by a comparison of the normalized reflectance ratio Rn to a plurality of normalized reflectance ratio Rn ranges, each range being associated with a particular type of media. For example, if the media sensor is calibrated with a perfectly diffuse media, then the normalized reflectance ratio Rn ranges might be as in the following table.
In one prior system designed to determine the print media type, it is possible to detect an empty paper tray by reflecting both specular and diffuse light components away from the sensor. However, such a design may be unreliable since the amount of detected light will be very small, similar to when a media sensor fails.
What is needed in the art is an improved media sensing apparatus that can detect the absence of print media reliably.
The present invention relates to an improved media sensing apparatus that can detect the absence of print media.
In one form thereof, the present invention is directed to a media sensing apparatus. The media sensing apparatus includes a media sensor including a light source for generating a light beam, and a diffuse detector positioned in relation to the light source for detecting diffuse light components reflected from a sheet of print media. A media support is provided having a detection portion. The detection portion is located such that the media sensor faces the detection portion. The detection portion is configured to direct specular light components reflected from the detection portion to the diffuse detector in an absence of the sheet of print media being interposed between the media sensor and the detection portion.
An advantage of the present invention is that it can be implemented relatively easily in any imaging device using a simple sensor that senses print media type.
Another advantage of the present invention is that the same sensor used to determine media type can be used to detect the absence of print media.
Another advantage is that the present invention can be implemented with little additional hardware costs in an imaging device having a preexisting sensor that senses the print media type.